DAMAGE AND EVOLUTION CHARACTERISTICS OF JURASSIC SOFT ROCK IN THREE GORGES RESERVOIR AREA UNDER WATER PRESSURE

To study the damage evolution characteristics of Jurassic soft rock at different reservoir water depth,the MTS triaxial compression and acoustic emission test of Jurassic argillaceous siltstone in Three Gorges Reservoir area is carried out under different water pressure states. The damage evolution equation considering initial damage caused by water is established based on acoustic emission ringing count. The mechanical deterioration characteristics,damage evolution stage and damage evolution characteristic value of Jurassic soft rock under water pressure are analyzed. The results show that,with the increase of water pressure(from 0MPa to 1MPa),the crack initial stress,damage stress,peak stress,residual stress and elastic modulus of soft rock all show a decreasing trend and decrease by 74.2%,66.9%,62.4%,43.4% and 51.9% respectively. The damage evolution process of Jurassic soft rock can be divided into damage formation stage,damage stability development stage,damage failure stage and post-damage failure stage. The damage evolution stage and crack development stage are basically synchronous. The damage evolution characteristic value can quantitatively reflect the influence of water pressure on Jurassic soft rock deterioration degree. These parameters have a good mathematical correlation with water pressure. The initial damage variable and crack initiation damage variable increase with the increase of water pressure. The crack initiation damage increment and the crack initiation damage strain decrease with the increase of water pressure. In the process of increasing water pressure,the values of initial damage variables and crack initiation damage variables are approaching gradually,the crack initiation damage increment and the crack initiation damage strain are gradually approaching to 0. These result show that the reservoir water pressure can cause different damage degrees to the Jurassic soft rock and can accelerate the crack development and failure process of the rock.